AMCEB.E AND DYSENTERY 153 



dissimilarity almost suggests different species, a fact 

 emphasizing the need of prolonged observations. 



Probably the most debated Entamoeba of the last 

 few years is E. histolytica, the main cause of amoebic 

 dysentery. The organism was first described by 

 Jiirgens in 1902, while a memoir, in which the sup- 

 posed life-cycle was minutely described, appeared by 

 Schaudinn in the following year. Schaudinn also 

 named the parasite, which probably had been 

 notified even prior to Jiirgens, though without special 

 naming. E. histolyiica has been examined since by 

 several writers, and it may be stated that the life- 

 cycle of the organism, as described by Schaudinn, is 

 really but one portion of the development of the 

 organism. Two other Entamcebae, previously de- 

 scribed as two different species, have now been 

 proved to be part of the life- history of E. histolytica, 

 instead of being distinct organisms. 



E. histolytica, according to Schaudinn, is from 

 25 to 30 /,& in diameter, though other observers 

 state that it is much smaller, a result easily explain- 

 able from further knowledge. It has a sharply 

 defined ectoplasm (Fig. 32, a) which it protrudes as 

 pseudopodia (Fig. 32, a) ; these are spiny when it is 

 burrowing into the wall of the intestine. The 

 endoplasm is slightly granular and passes into the 

 pseudopodia. Its nucleus varies in form and posi- 

 tion, and is not easily seen in the living organism. 



The enclosures in the cytoplasm are of interest. 

 They include various crystalloid substances (Fig. 

 32, e), bacteria and red blood-corpuscles, on which 

 the animal often feeds. Vacuoles (Fig. 32, d) are 



